Mark the dX and dB outputs of ConvGrad as OpSchema::Optional. (microsoft#5462)

* Mark the dB output of ConvGrad as OpSchema::Optional.

* Also mark dX as optional

Co-authored-by: Derek Murray <[email protected]>

Author: Derek Murray

orttraining/orttraining/core/graph/training_op_defs.cc

@@ -418,9 +418,9 @@ void RegisterTrainingOpSchemas() {
       .Input(0, "dY", "Gradient of output Y", "T")
       .Input(1, "X", "Input tensor", "T")
       .Input(2, "W", "Weight tensor", "T")
-      .Output(0, "dX", "Gradient of input X", "T")
+      .Output(0, "dX", "Gradient of input X", "T", OpSchema::Optional)
       .Output(1, "dW", "Gradient of W", "T")
-      .Output(2, "dB", "Gradient of B", "T")
+      .Output(2, "dB", "Gradient of B", "T", OpSchema::Optional)
       .AllowUncheckedAttributes()
       .TypeConstraint(
           "T",